f2fs: do not change the valid_block value if cur_valid_map was wrongly set or cleared

commit 35ee82ca133a58011e648a407d4ab13275c975d4 upstream.

Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>